This invention relates to a brake booster and the way a wall is attached to a hub to separate the interior housing of the brake booster into a front chamber and a rear chamber.
In vacuum brake boosters it is common for a movable wall to separate the interior of a housing into a front chamber and a rear chamber. Initial the movable wall was defined by a piston moving in a bore with a seal carried on the peripheral surface to seal the front chamber from the rear chamber. In an effort to reduce the resistance to movement of the piston, the seal was replaced by a rolling diaphragm such as disclosed in U.S. Pat. No. 3,279,327. In a further effort simplify a brake booster, the diaphragm was modified as disclosed in U.S. Pat. No. 5,207,142 by placing the diaphragm on the peripheral surface of the movable wall. However, in such vacuum brake boosters, the movable wall needed to be reinforced in order to transmit the operational force developed by a pressure differential acting thereon to the output push rod. It is therefor more common to provide the diaphragm with a metal backing plate through which the output force is transmitted into a hub for transmission to the output rod. In this type vacuum brake booster, a first bead on the rolling diaphragm is retained between flanges on front and rear shells that define the housing of the vacuum brake booster while a second bead is located in a groove on the movable wall. In an effort to provide for a common control valve for a vacuum brake booster, it was disclosed that a wall using a same cylindrical member could accommodate various sizes in a vacuum booster by changing the diameter of a backing plate and diaphragm as disclosed in U.S. Pat. No. 3,958,497. These vacuum brake boosters, as disclosed in the prior art, operate in a satisfactory manner, however, during assembly some specialized tools may be required to secure the movable wall to the hub for the control valve.
In the present invention a brake booster includes a wall for separating an interior of a housing into a front chamber and a rear chamber is attached to a cylindrical body of a hub through a deformation of an axial flange on a backing plate into a groove to hold a lip on a diaphragm in a sealing relationship with a flange on the cylindrical body.
According to this invention, the brake booster has a housing defined by joining a first shell with a second shell. The interior of the housing is separated into at least a first chamber and a second chamber by a wall. The wall a diaphragm with an interior lip connected to a peripheral surface on a cylindrical body of a hub and an exterior lip retained between flanges on the first and second shells. The cylindrical body has an axial bore that extends from a first end to a second end to retain a control valve. The control valve is designed to sequentially connect the first chamber with the second chamber in a first mode of operation and the second chamber to the environment in a second mode of operation. In the first mode of operation the fluid pressure between the first and second chambers is equal while in the second mode of operation, air presented to the second chamber, creates a pressure differential across the wall in response to an operational force being applied by an operator to initiate a brake application. The pressure differential acts on the wall to develop an output force that is communicated into the hub and after overcoming a return spring, the output force moves the hub to provide pistons in a master cylinder with an operational input force to effect a brake application. The cylindrical body of the hub is characterized by a radial flange that extends from the first end, a ledge that is located adjacent the flange, annular shoulder that extends from the peripheral surface and a groove located between the ledge and the annular shoulder. The groove has a depth adjacent the shoulder that is approximately equal to the height of the shoulder above the peripheral surface and a side wall that transitions from the groove to the ledge. The wall is characterized by a metal disc with an axial flange that extends from a first end and a diaphragm. The diaphragm has a lip with an annular slot therein that receives the axial flange on the metal disc. The lip is located on the ledge and a portion of the axial flange is deformed into the groove such that an axial seal is defined between the lip and the flange to prevent communication from the first chamber to the second chamber along the peripheral surface of the cylindrical body.
An advantage of this invention resides in a method through which a backing plate and diaphragm are attached to define a wall for a brake booster.
An object of this invention is to provide a vacuum brake booster with a wall attached to a hub by deforming a portion of an axial flange against a shoulder to develop an axial seal.